reduction division

Examples of reduction division in the following topics:

• Comparing Meiosis and Mitosis

  • For this reason, meiosis I is referred to as a reduction division.
  • There is no such reduction in ploidy level during mitosis.
  • Meiosis II is much more similar to a mitotic division.
  • Meiosis II is not a reduction division because, although there are fewer copies of the genome in the resulting cells, there is still one set of chromosomes, as there was at the end of meiosis I.
  • Meiosis II is, therefore, referred to as equatorial division.

• Introduction to Meiosis

  • Meiosis is the nuclear division of diploid cells into haploid cells, which is a necessary step in sexual reproduction.
  • Therefore, sexual reproduction includes a nuclear division that reduces the number of chromosome sets.
  • To achieve this reduction in chromosomes, meiosis consists of one round of chromosome duplication and two rounds of nuclear division.
  • Thus, meiosis I is the first round of meiotic division and consists of prophase I, prometaphase I, and so on.
  • Meiosis II, the second round of meiotic division, includes prophase II, prometaphase II, and so on.

• Gene Expression in Stem Cells

  • Symmetric division maintains stem cell lines and asymmetric division yields differentiated cells.
  • Stem cells are undifferentiated biological cells found in multicellular organisms, that can differentiate into specialized cells (asymmetric division) or can divide to produce more stem cells (symmetric division).
  • This mechanism is known as extrinsic asymmetric cell division.
  • The term asymmetric cell division usually refers to such intrinsic asymmetric divisions.
  • This diagram illustrates stem cell division and differentiation, through the processes of (1) symmetric stem cell division, (2) asymmetric stem cell division, (3) progenitor division, and (4) terminal differentiation.

• The Evolution of Mitochondria

  • Mitochondria arise from the division of existing mitochondria.
  • However, their reproduction is synchronized with the activity and division of the cell.
  • A third possible explanation is that mitochondria need to produce their own genetic material so as to ensure metabolic control in eukaryotic cells, which indicates that mtDNA directly influences the respiratory chain and the reduction/oxidation processes of the mitochondria.

• The Role of the Cell Cycle

  • Trillions of cell divisions subsequently occur in a controlled manner to produce a complex, multicellular human.
  • Single-celled organisms use cell division as their method of reproduction.
  • But what triggers a cell to divide and how does it prepare for and complete cell division?
  • Cells on the path to cell division proceed through a series of precisely timed and carefully regulated stages of growth, DNA replication, and division that produces two identical (clone) cells.
  • After four rounds of cell division, (b) there are 16 cells, as seen in this SEM image.

• Regulation of the Cell Cycle by External Events

  • External factors can influence the cell cycle by inhibiting or initiating cell division.
  • Both the initiation and inhibition of cell division are triggered by events external to the cell when it is about to begin the replication process.
  • A lack of HGH can inhibit cell division, resulting in dwarfism, whereas too much HGH can result in gigantism .
  • Crowding of cells can also inhibit cell division.
  • Another factor that can initiate cell division is the size of the cell; as a cell grows, it becomes inefficient due to its decreasing surface-to-volume ratio.

• The Major Divisions of Land Plants

• Types of Root Systems and Zones of Growth

  • The root tip has three main zones: a zone of cell division, a zone of elongation, and a zone of maturation.
  • The root tip can be divided into three zones: a zone of cell division, a zone of elongation, and a zone of maturation .
  • The zone of cell division is closest to the root tip and is made up of the actively-dividing cells of the root meristem, which contains the undifferentiated cells of the germinating plant.
  • A longitudinal view of the root reveals the zones of cell division, elongation, and maturation.
  • Cell division occurs in the apical meristem.

• Proto-oncogenes

  • Proto-oncogenes normally regulate cell division, but can be changed into oncogenes through mutation, which may cause cancers to form.
  • If the resulting daughter cells are too damaged to undergo further cell divisions, the mutation would not be propagated and no harm would come to the organism.
  • However, if the atypical daughter cells are able to undergo further cell divisions, subsequent generations of cells will probably accumulate even more mutations, some possibly in additional genes that regulate the cell cycle.

• Electrons and Energy

  • The transfer of electrons between molecules via oxidation and reduction allows the cell to transfer and use energy for cellular functions.
  • Instead, the electron shifts to a second compound, reducing the second compound (oxidation of one species always occurs in tandem with reduction of another).
  • The transfer of electrons between molecules via oxidation and reduction is important because most of the energy stored in atoms is in the form of high-energy electrons; it is this energy that is used to fuel cellular functions.